The invention of the ballpoint pen in the 20th century made carrying pens much more convenient. The ball was typically installed on one end of an ink “cartridge” or “refill” which could be removed from the pen for replacement. The main benefits were ease of refill of ink, cleanliness (reduced opportunity for ink spillage) and preservation of the ink supply (lower volatility of ink and less exposure of the ink to air). Part of the reduction in potential for ink spillage is the use of a ball, instead of a nib relying on capillary action, to apply the ink. Advances in ink technology increased the viscosity and lowered the volatility of the ink while at the same time reducing the time it takes the ink to set on the paper.
While ballpoint ink leaks far less easily than fountain pen ink, a ballpoint cannot be carried in clothing or accessories without risk of ink stains unless the point is covered by a removable and replaceable cap or contained within the pen (retractable). In some retractables, extension of the cartridge is effected by pressing a button on the end of the pen opposite the ball, with retraction accomplished by the press of a side button or pocket clip on the pen, or by pressing the end button again (the so-called “knock” pen). Other ballpoints extend and retract the ball by a twist of the pen.
Of all of these, only the cap pen and the twist pen dependably prevent inadvertent leak release into clothing or accessories. Their drawback, however, is that only an exceptionally dexterous person can open the pen with one hand. The knock pen and other push-button designs can be operated with one hand, but have the serious drawback of being subject to accidental extension of the ball in a pocket or handbag. Hence, a new pen is needed that may be operated with one hand but is not subject to accidental opening.
Also needed in conjunction with these needs is for the pen to be short in length so that it loosely fits in a pocket or accessory so that it may be easily retrieved.